Breast cancer screening with ultrasound image overlays

ABSTRACT

An adjunctive ultrasound mammography system and associated methods are described in which an ultrasound image being displayed near an x-ray mammogram image may be superimposed thereon or thereunder by a user for facilitating rapid comprehension of breast structures and detection of abnormalities therein. In one preferred embodiment, the x-ray mammogram image corresponds to a standard x-ray mammogram view, and the ultrasound image is a thick-slice image representing a thick-slice or slab-like portion of the breast volume substantially parallel to that standard x-ray mammogram view. In another preferred embodiment, the user is permitted to manually manipulate the registration of the ultrasound image with the x-ray mammogram image. It has been found that the manual registration process, which involves manual vernier adjustments responsive to perceived registration differences, can rapidly increase the radiologist&#39;s perception of the breast structures being displayed by both component images. Even though ultrasound images tend to have substantially different textures and feature emphases than x-ray images, the bimodal thick-slice/x-ray image, alone or in conjunction with the vernier registration process, can often expose or clarify tissue structures hidden in the separate component images, and can often obviate or explain certain noticed structures in the component images.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. Ser. No.10/160,836, filed May 31, 2002, which is a continuation-in-part ofInternational Application Ser. No. PCT/US01/43237, filed Nov. 19, 2001.Ser. No. PCT/US01/43237 claims the benefit of U.S. Provisional Ser. No.60/252,946, filed Nov. 24, 2000. Ser. No. 10/160,836 also claims thebenefit of U.S. Provisional Ser. No. 60/326,715, filed Oct. 3, 2001.This application also claims the benefit of Provisional Application No.60/415,385, filed Oct. 1, 2002. Each of the above-mentioned applicationsis incorporated by reference herein. The subject matter of the presentapplication is related to the subject matter of Ser. No.______[Atty.Dkt. No. 2692/63685-PCT-C] filed the same day as the presentapplication, which is incorporated by reference herein.

FIELD

[0002] This patent specification relates to medical imaging systems andprocesses. In particular, the present invention relates to theacquisition and display of breast ultrasound information in a mannerthat facilitates breast cancer screening.

BACKGROUND

[0003] Breast cancer is the most common cancer among women other thanskin cancer, and is the second leading cause of cancer death in womenafter lung cancer. The American Cancer Society currently estimates thatthere are about 203,500 new invasive cases of breast cancer per yearamong women in the United States and 39,600 deaths per year from thedisease. Prevention and early diagnosis of breast cancer are of foremostimportance. Because early breast cancer does not produce symptoms, theAmerican Cancer Society recommends a screening mammogram and a clinicalbreast examination every year for women over the age of 40.

[0004] X-ray mammography is currently the only imaging method for massscreening of breast cancer. In health maintenance organizations (HMOs)and other medical organizations, specialized x-ray mammography clinicsdesigned for high patient throughput are being increasingly used toscreen as many women as possible in a time and cost efficient manner.Numerous studies have shown that early detection saves lives andincreases treatment options. Recent declines in breast cancer mortalityrates (e.g., 39,600 deaths in 2002 versus 41,200 in 2000) have beenattributed, in large part, to the regular use of screening x-raymammography.

[0005] It has been found that the use of ultrasound mammography(sonomammography) in conjunction with conventional x-ray mammography candrastically increase the early breast cancer detection rate. Whereasx-ray mammograms only detect a summation of the x-ray opacity ofindividual slices over the entire breast, ultrasound can separatelydetect the acoustic impedance of individual slices of breast tissue, andtherefore may allow detection of breast lesions where x-ray mammographyalone fails.

[0006] However, as discussed in Ser. No. 10/160,836, supra, despitestrong evidence that use of independent ultrasound examination wouldimprove early breast cancer detection and therefore save lives,substantial resistance against such use currently exists in the medicalindustry, including the radiologists themselves, and among policymakers.As used herein, the term “radiologist” generically refers to a medicalprofessional that analyzes medical images and makes clinicaldeterminations therefrom, it being understood that such person might betitled differently, or might have differing qualifications, depending onthe country or locality of their particular medical environment. Severalinterrelated factors are often cited, including: (i) the false negative(missing) rate of independent ultrasound examination is unknown, (ii)the false positive rate of independent ultrasound examination is knownto be very high, leading to an increase in unneeded patient callbacksand biopsies, (iii) lack of image acquisition standardization, leadingto variability among different operators and radiologists, (iv) theadditional time and equipment required to conduct the ultrasoundexamination, leading to an increase in cost, (v) most if not allradiologists are not trained to read screening ultrasound images, whichcontain features not found in current breast imaging textbooks or taughtin current medical school courses, leading to a potential increase infalse negative (missing) rate and in the additional radiologist timerequired to analyze the ultrasound images, and (vi) the additionaltraining and clinical experience that would be required for theradiologist to properly analyze the ultrasound images.

[0007] Various schemes have been proposed for processing and presentingbreast ultrasound information in conjunction with x-ray mammograminformation for use in breast cancer detection environments. In U.S.Pat. No. 5,938,613, which is incorporated by reference herein, a methodand apparatus for performing sonomammography and enhanced x-ray imagingis discussed in which ultrasound equipment is integrated withmammography equipment to generate ultrasonic images of the breast thatare in geometric registration with an x-ray mammogram. An x-raymammogram image of an immobilized breast is acquired and, while thebreast is still immobilized, an ultrasound scan is acquired using anautomated ultrasound probe translation mechanism. Cross-sectionalultrasonic slices are summed across the entire breast to form atwo-dimensional ultrasound image, which is then overlaid onto thedigitized x-ray image for viewing by the radiologist. Precise geometricregistration between the ultrasound image and the x-ray mammogram isautomatically provided because the breast is immobilized between imagingprocedures and because the coordinates of the ultrasound probe are knownduring each scan. The radiologist is permitted to instantiate certainalgorithms such as digital subtraction between the registered medicalimages.

[0008] However, the '613 patent is deficient in several respects withrespect to the practical, real-world factors associated with the currentresistance against the use of ultrasound in mass breast cancer screeningenvironments. For example, the large base of currently installed x-rayimaging systems would require substantial retooling to accommodate themechanical apparatus of the '613 patent that keeps the breastimmobilized between imaging procedures and that performs the automatedultrasound scans. As another example, by displaying a summationultrasound image of all breast slices together, the '613 method deprivesthe radiologist of the ability to view individual planes inside thebreast. More generally, the computer-registered, static overlay of thesummation ultrasound image onto the x-ray image affords only a limitedamount of ultrasonic information to the radiologist as compared to theactual amount of ultrasonic data actually acquired, and affords onlylimited perception by the radiologist of structures within the breast.

[0009] In U.S. Pat. No. 5,662,109, a method and system formulti-dimensional imaging and analysis for early detection of diseasedtissue is discussed. Ultrasound scans of a breast are processed intomultiple layers of two-dimensional images, thus yielding athree-dimensional data set. This data set and a two-dimensional x-raymammogram are input to an enhancer that performs one or more “datafusion” algorithms to generate a three-dimensional representation of thebreast for viewing. The enhancer includes a registration module thatexpands and/or reduces dimensions of the data to register and align theultrasound and mammographic images.

[0010] However, it is not believed that the various three-dimensionalviews of the “fused” data discussed in the '109 patent, such as theperspective view shown in FIG. 1 thereof, would be useful to a typicalradiologist trained in conventional x-ray mammography methods. Asdescribed supra, radiologists typically spend many years developingexpertise in analyzing a very particular set of two-dimensional x-raymammographic data taken from standardized views, most commonly thecraniocaudal (CC) and mediolateral oblique (MLO) views. It is believedthat most radiologists would be reluctant to “start over again” with anentirely new, different way of viewing the complex structures of abreast, and that the medical industry would likewise be reluctant toforce radiologists to accept these viewing methods.

[0011] In view of the above discussions, it would be desirable toprovide an adjunctive ultrasound mammography system that integratesultrasound mammography into current breast cancer screeningmethodologies.

[0012] It would be further desirable to provide an adjunctive ultrasoundmammography system that displays breast ultrasound information in amanner that facilitates the radiologist's perception of internal breaststructures that may not be readily apparent in an x-ray mammogram, whilealso being able to confirm the radiologist's perception of internalbreast structures that are apparent in the x-ray mammogram.

[0013] It would be even further desirable to provide an adjunctiveultrasound mammography system that displays breast ultrasoundinformation in a manner that supplements, rather than replaces,conventional x-ray mammogram viewing methods, thereby increasing thelikelihood of adoption by both individual radiologists and the medicalindustry.

[0014] It would be even further desirable to provide an adjunctiveultrasound mammography system that takes little or no specialfamiliarization or training from the radiologist in order to effectivelyview breast ultrasound information.

SUMMARY

[0015] An adjunctive ultrasound mammography system and associatedmethods are provided including an adjunctive ultrasound display systemconfigured to allow flexible, intuitive, and interactive viewing ofbreast ultrasound information in a manner that complements x-raymammogram viewing. An ultrasound image of a breast is displayed near anx-ray mammogram image of the breast, the adjunctive ultrasound displaysystem allowing for superposition of the ultrasound image over the x-raymammogram image, or vice-versa, for facilitating rapid comprehension ofbreast structures and detection of abnormalities therein. In onepreferred embodiment, the x-ray mammogram image corresponds to astandard x-ray mammogram view, and the ultrasound image is a thick-sliceimage representing a thick-slice or slab-like portion of the breastvolume substantially parallel to that standard x-ray mammogram view. Inanother preferred embodiment, the user is permitted to perform manualvernier adjustments of the registration of the ultrasound image with thex-ray mammogram image.

[0016] Advantageously, thick-slice ultrasound images corresponding tostandard x-ray mammogram view planes are of immediate and familiarsignificance to the radiologist, both as stand-alone images and ascomponents of bimodal ultrasound/x-ray images. Moreover, it has beenfound that the manual vernier registration adjustment process itself, inwhich the radiologist shifts the relative positions of the componentimages responsive to perceived registration differences, can rapidlyincrease the radiologist's perception and appreciation of the breaststructures being displayed by both component images. Even thoughultrasound images tend to have substantially different textures andfeature emphases than x-ray images, the resulting bimodal image, aloneor in combination with the manual vernier registration adjustmentprocess, can often expose or clarify tissue structures that may behidden or less apparent in the separate x-ray mammogram and/orultrasound images, and can often obviate or explain certain noticedstructures in the separate x-ray mammogram and/or ultrasound images.

[0017] Preferably, an array of thick-slice images is displayed to theradiologist representing different thick-slice portions of the breast,and the radiologist can manually superimpose any one of them over thex-ray mammogram image, or can manually superimpose the x-ray mammogramimage over any one of them. In one preferred embodiment, both the x-raymammogram image and the ultrasound image are displayed on the samescreen of a high-resolution monitor, and a pixelwise digital mixingalgorithm is used to achieve image superposition. Preferably, a mixingalgorithm is selected that approximates the visual effect of (i) placinga conventional x-ray mammogram film on a light box, and (ii)superimposing a second transparency thereon containing a printed versionof the thick-slice ultrasound image. However, the incorporation of anyof a variety of digital mixing algorithms is within the scope of thepreferred embodiments, including those that permit dynamic adjustment ofone or more mixing parameters by the radiologist, and including bothpixelwise and neighborhood-based mixing algorithms.

[0018] In other preferred embodiments, the component medical images arepresented in any of a variety of physical configurations that permit theuser to overlay them to form a bimodal image and to perform fineregistration adjustments. The component medical images may exist onx-ray film, as lightbox backprojections, on high-brightness computermonitors, on transparent or opaque hardcopies, on subtractive liquidcrystal displays, and/or on other types of image displays, and indifferent combinations thereof, provided that image superposition ispossible. Any of a variety of mechanisms may be used to physicallymove/overlay the medical images and to provide manual vernier adjustmentcapability, ranging from hand manipulation of hardcopy images tocomputerized click-and-drag techniques.

[0019] In one preferred embodiment in which the ultrasound image isdisplayed in electronic format, user inputs are provided for allowingdynamic adjustment of (i) the thickness of the thick-slice image, i.e.,the thickness of the slab-like region of the breast that is integratedinto a single two-dimensional thick-slice image, and (ii) thick-sliceimage elevation, i.e., the vertical elevation of the slab-like regionwithin the breast volume. In one preferred embodiment, the positioningof the overlying image onto the underlying image is an entirely manualprocess, the radiologist manually performing both (i) preliminary orcoarse registration, i.e., moving the images from their initialpositions onto each other, and (ii) vernier registration, i.e.,perfecting the registration of the images. In an alternative preferredembodiment, preliminary registration is provided automatically by thedisplay system using any of a variety of known methods, such that theradiologist only needs to perform the vernier registration step.Preferably, in an adjunctive ultrasound system using ultrasound overlaysaccording to a preferred embodiment, the ultrasound image information isprovided to the radiologist on a supplementary, as-needed basis, withoutinterfering with the radiologist's primary task of analyzing x-raymammograms. This is believed to be advantageous from a strategicmedical-community acceptance viewpoint, because entrenched radiologistswill not be “forced” to use the ultrasound information. Once calledupon, however, it is expected that the convenient, easy-to-use,intuitive ultrasound information viewing system according to thepreferred embodiments will attract many radiologists to its use ineveryday mass breast cancer screening activities.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 illustrates a conceptual diagram of a system and method forbreast cancer screening using adjunctive ultrasound mammographyaccording to a preferred embodiment;

[0021]FIG. 2 illustrates a conceptual diagram of a first medical imageof a breast;

[0022]FIG. 3 illustrates a conceptual diagram of a second medical imageof a breast;

[0023]FIG. 4 illustrates a conceptual diagram of a bimodal medical imageformed from the medical images of FIGS. 2 and 3;

[0024]FIG. 5 illustrates an adjunct ultrasound display at differentintervals during an overlay of an ultrasound image onto an x-raymammogram image;

[0025]FIG. 6 illustrates steps corresponding to a method for breastcancer screening using an x-ray mammogram with adjunct ultrasoundoverlays according to a preferred embodiment;

[0026]FIG. 7 illustrates a conceptual diagram of varying thick-sliceelevation and thick-slice thickness using a dynamic control mechanismaccording to a preferred embodiment;

[0027]FIG. 8 illustrates an adjunct ultrasound display according to apreferred embodiment displaying an ultrasound thick-slice image;

[0028]FIG. 9 illustrates an adjunct ultrasound display according to apreferred embodiment displaying a remapped version of the ultrasoundthick-slice image of FIG. 8;

[0029]FIG. 10 illustrates an adjunct ultrasound display according to apreferred embodiment displaying a digital x-ray mammogram adjacent tothe ultrasound thick-slice image of FIG. 9;

[0030]FIG. 11 illustrates an adjunct ultrasound display according to apreferred embodiment displaying the digital x-ray mammogram of FIGS.9-10 as it is moved toward the ultrasound thick-slice image of FIGS.9-10 for mixing therewith;

[0031]FIG. 12 illustrates an adjunct ultrasound display according to apreferred embodiment displaying a bimodal image of a digital x-raymammogram superimposed upon an ultrasound thick-slice image and inapproximate registration therewith;

[0032]FIG. 13 illustrates an adjunct ultrasound display according to apreferred embodiment displaying the bimodal image of FIG. 12 as adjustedto allow its digital x-ray mammogram component to predominate over theultrasound thick-slice image component; and

[0033]FIG. 14 illustrates an adjunct ultrasound display according to apreferred embodiment displaying the bimodal image of FIG. 12 as adjustedto allow its ultrasound thick-slice image component to predominate overits digital x-ray mammogram component.

DETAILED DESCRIPTION

[0034]FIG. 1 illustrates a conceptual diagram of a system 100 andassociated methods for breast cancer screening using adjunctiveultrasound mammography according to a preferred embodiment. Many aspectsof the system 100 are also described in Ser. No. 10/160,836, supra.Adjunctive ultrasound mammography refers to the acquisition and displayof breast ultrasound information during the breast cancer screeningprocess in a manner that supplements x-ray mammogram information. System100 comprises an ultrasound scanning station 102, a computer network104, an adjunctive ultrasound server 106, and an adjunctive ultrasoundscreening station 108. Ultrasound scanning station 102 comprises anultrasound scanning apparatus 110 for facilitating breast ultrasoundscans of the patient 112 by an ultrasound technician 114. An ultrasoundprobe 116 is used to scan a breast of the patient 112, with reflectedacoustic interrogation signals being processed by an ultrasound machine118.

[0035] Preferable to the ultrasound scanning station 102 of FIG. 1 areultrasound scanning unit described more fully in Ser. Nos. 60/415,385and Ser No.______[my ref: U037], supra.

[0036] The ultrasound scanning apparatus 110 supports and maintains thebreast during the ultrasound scanning process. According to a preferredembodiment, the ultrasound scanning apparatus 110 also flattens thebreast along a plane parallel to a standard x-ray mammogram view planesuch that resulting ultrasound images correspond more closely tostandard x-ray mammogram images. In the example of FIG. 1, the standardx-ray mammogram view is the craniocaudal (CC) view. While describedherein with respect to the CC view for simplicity and clarity ofexplanation, it is to be appreciated that the preferred embodiments arereadily applied to the mediolateral oblique (MLO) view or to standard orcustom x-ray mammogram views.

[0037] Although not shown in FIG. 1, the patient 112 also undergoes astandard x-ray mammography procedure in addition to the ultrasoundmammography procedure. The x-ray mammogram is usually taken during thesame office visit as the ultrasonic mammography scans, although thescope of the preferred embodiments is not so limited. The ultrasoundtechnician 114 may be the same person or a different person as the x-raytechnician who performs the x-ray mammography procedure.

[0038] If the ultrasound probe 116 is manipulated by hand, as in theembodiment of FIG. 1, a position sensing system (not shown) is used totrack the probe position such that the acquired ultrasound frames may beprocessed into a three-dimensional volumetric representation of thebreast. It is generally preferable, however, that the ultrasound probe116 be machine-manipulated and controlled so as to provide reliable,consistent ultrasound scans. The ultrasound scans should be ofsufficient resolution and taken at small enough intervals such that thethree-dimensional volumetric representation has sufficient resolution toenable computer-aided diagnosis (CAD) algorithms to perform effectively,and such that both individual ultrasound slices and thick-slice imagesare of sufficient resolution to enable meaningful screening assistanceto the radiologist.

[0039] As will be described further infra, the raw ultrasound scans maybe taken directly in the standard x-ray mammogram view plane, or mayalternatively be taken from a different orientation. When the rawultrasound scans are taken directly in the standard x-ray mammogram viewplane, each individual ultrasound slice is computed directly from anacquired two-dimensional ultrasound image or ultrasound frame. When theraw ultrasound scans are taken from a different orientation, eachindividual ultrasound slice corresponds to a plane of voxels (volumeelements) in a three-dimensional volumetric representation of thebreast, the plane of voxels being oriented in a direction parallel tothe standard x-ray mammogram view plane. Most commonly, thethree-dimensional volumetric representation of the breast is computedfrom the raw ultrasound scans, and then the individual ultrasound sliceis extracted therefrom. However, in other preferred embodiments such asthose described in Ser. No. 60/326,715, supra, it is not alwaysnecessary to reconstruct the entire three-dimensional volumetricrepresentation to compute the individual ultrasound slices. Stated moregenerally, if the raw ultrasound scans are taken in planes directlyparallel to a plane of interest (CC, MLO, or a different “custom” planeof importance), each individual ultrasound slice is computed directlyfrom an acquired two-dimensional ultrasound image or ultrasound frame,whereas if the raw ultrasound scans are taken from directions differentthan the plane of interest, each individual ultrasound slice correspondsto a plane of voxels in a three-dimensional volumetric representation ofthe breast in a direction parallel to the plane of interest.

[0040] Ultrasound machine 118 may generally comprise any commerciallyavailable ultrasound machine having sufficient resolution, speed, andnetwork connectivity to achieve the functionalities described herein.During or after the ultrasound scanning process, the raw ultrasound datais provided across the computer network 104 to the adjunctive ultrasoundserver 106, where the raw ultrasound data is processed into adjunctiveultrasound data that will be made available to the screeningradiologist, the adjunctive ultrasound data including ultrasound slices,thick-slice images, vibrational Doppler imaging (VDI) images, CADoutputs, and other useful information. It is to be appreciated that theprocessing of the raw ultrasound data into the adjunctive ultrasounddata may be performed by any of a variety of different computing devicescoupled to the computer network 104 and then transferred to theadjunctive ultrasound server 106.

[0041] Although many different variations are within the scope of thepreferred embodiments, in the example of FIG. 1 the adjunctiveultrasound screening station 108 comprises four display monitors, eachdedicated to a particular standard x-ray mammogram view for each breast.On a first display monitor 120, a right CC x-ray mammogram image 122 isdisplayed, with a plurality of ultrasound thick-slice thumbnail images124 being distributed in an arc-like pattern therearound as shown inFIG. 1. The thumbnail thick-slice images 130 represent thick-sliceportions of the left breast volume oriented parallel to the CC viewplane. A second display monitor 126 displays a left CC x-ray view 128and associated ultrasound thick-slice thumbnails 130, a third displaymonitor 132 displays a right MLO x-ray view 134 and associatedultrasound thick-slice thumbnails 136, and a fourth display monitor 138displays a left MLO x-ray view 140 and associated ultrasound thick-slicethumbnails 142. For simplicity and clarity of explanation, only the leftCC view monitor 126 is detailed herein, it being understood that similardescriptions apply to the other standard x-ray mammogram views.

[0042] Generally speaking, a thick-slice image is an integration of aplurality of substantially parallel individual ultrasound slices used torepresent a slab-like or thick-slice volume of the breast. The thicknessof the slab-like or thick-slice volume may lie, for example, in therange of 2 mm to 20 mm, although the scope of the preferred embodimentsis not so limited. Techniques for integrating the component ultrasoundslices into thick-slice images according to the preferred embodimentsinclude arithmetic averaging, geometric averaging, reciprocal averaging,exponential averaging, and other averaging methods, in each caseincluding both weighted and unweighted averaging techniques. Othersuitable integration methods may be based on statistical properties ofthe population of component ultrasound slices at common locations, suchas maximum value, minimum value, mean, variance, or other statisticalalgorithms. Generally speaking, the ultrasound thick-slice images andthumbnails described herein are similar to those described in Ser. No.10/160,836, supra.

[0043] In the preferred embodiment of FIG. 1, at the outset of thedisplay process, the ultrasound thick-slice thumbnails 130 are ofsufficient number and thickness to represent the entire breast volume.For example, if the compressed breast volume has a total elevation of 6cm, there can be six individual thick-slice thumbnails eachcorresponding to 1 cm slab-like regions within the breast. The x-raymammogram image 128 is preferably displayed at full-scale. If thedisplay monitor 126 is sufficiently large, the thick-slice thumbnailscan be replaced with full-scale thick-slice images if desired.

[0044] Adjunctive ultrasound screening station 108A further comprises acontrol panel positioned near or integrated with each display monitor120, 126, 132, and 138. In the simple example of FIG. 1 a keyboard 140,a mouse 142, and a joystick 144 are provided through which user controland the manual image manipulations infra are achieved. It is to beappreciated that the user controls and manual image manipulationsdescribed herein are in addition to the user controls and other featuresdescribed in Ser. No. 10/160,836, supra.

[0045] FIGS. 2-4 are conceptual diagrams intended to communicate, in asimplified hypothetical setting, the analytical assistance that anoverlay of two medical images of two different modalities can provide.FIG. 2 illustrates a conceptual diagram of a first medical image 200 ofa breast according to a first imaging modality (e.g., x-ray mammogram).FIG. 3 illustrates a conceptual diagram of a second medical image 300 ofa breast according to a second imaging modality (e.g., ultrasound). FIG.4 illustrates a conceptual diagram of a bimodal medical image 400 formedby a superposition of the medical images 200 and 300. As indicated inFIG. 4, some of the features that are salient in one medical image(e.g., suspect regions 202 and 302) do not become enhanced or clarifiedby corresponding locations in the other image, and this information maybe useful in determining a false positive or in further characterizationof a suspect region. Conversely, some features that may not beparticularly evident in either medical image may become apparent whenthe images are superimposed, as represented by the suspect region 402.Once again, it is to be appreciated that the example of FIGS. 2-4 ishypothetical in nature for communicating one or more principlesaccording to the preferred embodiments, and is not a literal portrayalof breast images. However, analogous advantages apparent to the trainedeye can be enjoyed by overlay of ultrasound thick-slice images and x-raymammogram images of a breast, or vice versa, in accordance with thepreferred embodiments.

[0046] Thus, in one preferred embodiment, one or more ultrasoundthick-slice images are superimposed onto a corresponding x-ray mammogramview, the thick-slice images representing a slab-like volume of thebreast taken parallel to a standard x-ray mammogram view. In otherpreferred embodiment, one or more ultrasound thick-slice images aresuperimposed onto a corresponding x-ray mammogram view, the thick-sliceimages representing a slab-like portion of the breast that issubstantially less thick than the entire breast volume. This providesthe advantage, not offered by the summation ultrasound image of U.S.Pat. No. 5,938,613, supra.

[0047] In yet another preferred embodiment, one or more ultrasoundimages of the breast are superimposed onto a corresponding x-raymammogram view in a manner that allows for manual vernier adjustments ofthe registration of the images. It has been found that the manualvernier registration adjustments of the ultrasound images with thecorresponding x-ray mammogram image is of substantial benefit in imageanalysis. In particular, it rapidly increases the viewer's perceptionand appreciation of breast structures being displayed by both componentimages, as compared to when (i) the component images are presentedside-by-side, and (ii) the component images are displayed in fixedregistration. Although precise explanations might well be left tocognitive scientists, it is believed that the generally amorphous natureof the breast images makes it difficult, when placed side-by-side, tomentally carry across distance and proportion information from one imageto the other. This problem is alleviated somewhat when the images aresuperimposed and displayed in fixed registration with each other.However, especially with the medical image modalities at hand, it isstill often difficult to perceive which component image is displayingwhich localized patterns in the fixed-registration bimodal image. Whenmanual, vernier registration adjustments are performed according to thepreferred embodiments, the subtle shifts of entire localized patternsresponsive to the user's own adjustments can substantially enhancecomprehension of the different localized patterns in both componentimages and in the overall bimodal image.

[0048]FIG. 5 illustrates the adjunct ultrasound display monitor 126 atdifferent intervals during an overlay of an ultrasound image onto anx-ray mammogram image 128. In frame (a), the user first moves a cursor502 over a particular ultrasound thick-slice thumbnail of interest. Inframe (b), upon clicking the thick-slice thumbnail, the thumbnail isexpanded to a full ultrasound thick-slice image 504 having the samespatial scale as the x-ray mammogram image 128. At frame (c), the userclicks-and-drags the ultrasound thick-slice image 504 over toward thex-ray mammogram image 128. At frame (d), a bimodal image 506 isdisplayed, with the user performing small, manual adjustments to theregistration of the two component images forming the bimodal image. Asthe component images begin to overlap in frame (c), a mixing algorithmdescribed further infra is used that approximates the visual effect ofplacing a conventional x-ray mammogram film on a light box, andsuperimposing a second transparency thereon containing a printed versionof the thick-slice ultrasound image, although in general any of avariety of different mixing algorithms can be used to superimpose thecomponent images.

[0049]FIG. 6 illustrates steps for breast cancer screening using anx-ray mammogram with adjunct ultrasound overlays according to apreferred embodiment. The steps of FIG. 6 are described with respect toa single x-ray mammogram view/breast pair (e.g., CC view for leftbreast), it being understood that analogous steps for the otherbreast/view pairs are being carried out serially or in parallel with thesteps of FIG. 6. At step 602, an array of ultrasound thick-slicethumbnails is displayed near an x-ray mammogram image. At step 604, theuser selects an ultrasound thick-slice thumbnail of interest. At step606, the spatial scale of the ultrasound thick-slice thumbnail isincreased to the same scale as the x-ray mammogram image. At step 608,the thick-slice ultrasound image is remapped, if necessary, to becomplementary to the display values of the x-ray mammogram image.

[0050] At step 610, the thick-slice image is moved over the x-raymammogram image in approximate or “starter” registration therewith.While in the embodiments of FIG. 5 this is described in terms of amanual click-and-drag process, the scope of the preferred embodiments isnot so limited. In an alternative preferred embodiment, this step isperformed automatically by the adjunctive ultrasound display systemusing methods known in the art, thereby saving radiologist time.Automated registration methods include those based on skin lines, nippleposition, chest wall position, artificial external markers, naturalinternal feature markers such as visible microcalcifications, and/orother methods. Methods based on artificial external markers includethose using a single “BB” or similar marker placed near the nipple, aswell as those using three or more BBs. Where multiple artificial markersare used, the scaling of the component images may be contracted orexpanded in one or both directions as necessary to get all of themarkers to line up.

[0051] At step 612 the user performs manual vernier registrationadjustments. When the previous initial registration step 610 isperformed automatically rather than by manual manipulation, the vernieradjustments may be based on perceived registration differences in theinitial registration. On the other hand, even if the initialregistration is very good or perfect, the user still manipulates thecomponent images to be slightly out-of-registration, and then moves themback into registration, in order to experience the benefits of thevernier image manipulations described supra. At step 614 the user mayoptionally perform mixing parameter adjustments as described infra withrespect to FIGS. 13-14. At step 616 the user may optionally performthick-slice elevation and thickness adjustments according to a “rollingthick-slice” method described infra with respect to FIG. 7. At step 618the user may choose to continue the adjustment and analysis process ormay proceed to another image view or thick-slice image.

[0052]FIG. 7 illustrates a top view of the joystick control 144 of theadjunctive ultrasound screening station 108 of FIG. 1, along with aconceptual side view of a breast 702 and a slab-like thick-slice region704 therein, for further describing the “rolling thick-slice” method ofstep 616 of FIG. 6, supra. For the CC view, when the joystick 144 ismoved forward (frame (a)) or backward (frame (b)), the elevation of thethick-slice region 704 relative to a bottom compression plate isadjusted upward or downward, respectively, within the breast volume. Forthe MLO view, this elevation metric corresponds to a distance from thevertically-oriented compression plane for that view. More generally, ifa non-standard plane is used, the elevation corresponds to a distancefrom one of the compression plates used to compress the breast. When thejoystick 144 is moved right (frame (c)) or left (frame (d)), thethickness of the slab-like region whose data is used to form thethick-slice image is increased or decreased, respectively. Accordingly,the user may easily navigate throughout the breast volume, and mayeasily select between thinner and thicker-slice regions to compare tothe x-ray mammogram. The thick-slice ultrasound image gently morphsalong a continuum of two-dimensional representations in an intuitivemanner that allows the radiologist to readily navigate the breast inboth a positional sense (elevation) and abstractional sense (slabthickness).

[0053] FIGS. 8-14 illustrate a user display 800 according to a preferredembodiment at different points in a medical image superposition processaccording to a preferred embodiment. The user display 800 comprises aset of selection buttons 802, a patient identification display 822, andone or more medical images as described herein. Generally speaking, inaddition to the capabilities described herein, all of the capabilitiesof the user display of Ser. No. 10/160,836, supra, are incorporated intothe user display 800, such as the ability to display multiple thumbnailthick-slice images, select and expand a given thumbnail into afull-scale image, analyze individual slices and cine-presentationsthereof throughout the breast volume, etc., as facilitated by theselection buttons 804-820. In the preferred embodiment of FIGS. 8-14, itis an x-ray mammogram image that is manually superimposed over a staticthick-slice ultrasound image.

[0054]FIG. 8 illustrates the user display 800 after a particularthick-slice image from a particular zone for the RCC view has beenselected and expanded into the ultrasound image 824. The ultrasoundimage 824 is an 8-bit grayscale image with the gray scale selected to bereminiscent of a film-based x-ray mammogram as displayed on a light box,i.e., brightest=255=D_(max)=high acoustic echo and darkest=0=lowacoustic echo.

[0055]FIG. 9 illustrates the user display 800 upon user pressing of afirst superposition key, such as the keyboard letter “I.” Responsive tothis command, the ultrasound image 824 is inverted such thatbrightest=255=D_(max)=low acoustic echo and darkest=0=high acousticecho.

[0056]FIG. 10 illustrates the user display 800 upon user pressing of asecond superposition key, such as the keyboard letter “M.” Responsive tothis command, an x-ray mammogram image 1002 is displayed near theultrasound image 902. The x-ray mammogram image 1002 is an 8-bitgrayscale image with the gray scale set to mimic the appearance of afilm-based x-ray mammogram as placed on a light box, i.e.,brightest=255=D_(max)=highly radio-opaque and darkest=0=highlyradio-transparent.

[0057]FIG. 11 illustrates the user display 800 as the user manuallymoves the x-ray mammogram image 1002 over the ultrasound image 902. Inone preferred embodiment, the user manually causes lateral movement bypressing of the LEFT and RIGHT arrow keys of the keyboard and verticalmovement by pressing the UP and DOWN arrows of the keyboard. At areas ofimage overlap, a pixelwise mixing algorithm is used to achievesuperposition of the medical images. In one preferred embodimentillustrated in FIGS. 11-14, the mixing algorithm is given by Eq. (1)below, where (x,y) represents the coordinates of the pixel in question,u(x,y) is the value of the inverted ultrasound image 902 at thatlocation, m(x,y) is the value of the x-ray mammogram image 1002 at thatlocation, d(x,y) is the ultimate output display value at that location,and F_(mix) is a scalar mixing factor valued between zero and unity:

d(x,y)=F _(mix) m(x,y)+(1−F _(mix))·u(x,y)  {1}

[0058] Preferably, the mixing factor F_(mix) is dynamicallyuser-adjustable, but will be assigned a default starting value of about0.5. Any of a variety of mixing algorithms may be used in accordancewith the preferred embodiments, and may be varied according to thespecific display hardware used and the quality and dynamic range of themedical images used. In another preferred embodiment, the mixingalgorithm is designed to closely emulate a film-based superpositionscenario comprising (i) a light box, (ii) a standard film-based x-raymammogram placed thereon (dark=radio-transparent, clear=radio-opaque),and (iii) an ultrasound image printed on a clear film placed thereon,the ultrasound image being printed such that dark=high acoustic echo andclear=low acoustic echo. This algorithm is given by Eq. (2) below, whereD_(max) is the brightest value available on the display monitor:

d(x,y)=D _(max) *[m(x,y)/D _(max) ]* [u(x,y)/D _(max))]  {2}

[0059]FIG. 12 illustrates the user display 800 as registration of thecomponent images is substantially achieved to form a bimodal image 1202.While viewing the bimodal image 1202, the user will usually beperforming small manual adjustments of the registration of the componentimages by using the arrow keys, as described supra. During this process,the user may adjust the elevation and/or thickness of the thick-sliceultrasound image component in a “rolling thick slice” method describedsupra with respect to FIG. 7. Additionally, the mixing factor F_(mix)may be dynamically adjusted, for example by using the “+” and “−”keyboard keys, so as to let one or the other of the component medicalimages predominate.

[0060]FIG. 13 illustrates the user display 800 as the mixing factorF_(mix) is adjusted closer to zero to let the x-ray mammogram imagecomponent predominate. FIG. 14 illustrates the user display 800 as themixing factor F_(mix) is adjusted closer to unity to let the ultrasoundimage component predominate.

[0061] It is to be appreciated that those preferred embodimentsdescribed supra in which both component images are displayed inelectronic format are presented by way of non-limiting example only, andany of a variety of other component medical image display and bimodalimage formation methods is within the scope of the preferredembodiments. For example, in another preferred embodiment, the x-raymammogram is provided on a conventional x-ray film and placed on alightbox, the lightbox being capable of backprojecting an ultrasoundimage onto its display surface. After reviewing the x-ray film in aconventional fashion, the radiologist may then activate thisbackprojection feature and thereby view an overlay of the x-raymammogram image on the ultrasound image. In another preferredembodiment, a high-brightness computer display is used to illuminate anx-ray film for conventional viewing in a first configuration, and todisplay an ultrasound image in a second configuration that projectsthrough the x-ray film to achieve an overlay of the x-ray mammogramimage on the ultrasound image. In still another preferred embodiment,the x-ray mammogram is displayed digitally on a monitor or backprojectedonto a light box, while the ultrasound image is printed onto atranslucent film and placed on the monitor or light box.

[0062] In still another preferred embodiment, a standard film-basedx-ray mammogram is placed on a lightbox, and an ultrasound image printedon a clear film is placed thereon and manually manipulated by the user.In such preferred embodiment, several thick-slice ultrasound images areprinted on separate transparent sheets, which can be interchanged by theuser as needed to achieve elevation variations, and which can bedoubled-up or tripled-up as needed to represent thicker thick-sliceregions of the breast volume.

[0063] In each case, the overlying and underlying medical images shouldbe complementary to each other, and should be amenable to manual vernierregistration adjustment by the user. Any of a variety of manual vernierregistration adjustment techniques may be employed between the overlaidimage and the underlying image.

[0064] For those preferred embodiments in which a first medical image isprovided in film or other hardcopy format while a second medical imageis provided in electronic display format, a bar code reader is includedin the viewing station hardware. The bar code reader reads a bar codethat is placed on each hardcopy image, using that bar code informationto locate and access the second medical image from the system database.

[0065] Any of a variety of manual vernier registration adjustmenttechniques may be employed between the overlaid image and the underlyingimage, including touch-screen control, mouse or joystick control,trackball control, mechanical control, other techniques, or acombination of these techniques. For example, where both the x-ray imageand ultrasound image are electronically displayed on the same displaymonitor, a click-and-drag technique using a computer mouse or joystickmay be used. If one or both of the component images is on film or otherhardcopy format, the radiologist may slide the overlying image acrossthe underlying image by hand. Alternatively or in conjunction therewith,where the underlying image is achieved by backprojection or computerdisplay, the underlying image may be manually shifted using by computermouse click-and-drag, joystick, or trackball control.

[0066] Whereas many alterations and modifications of the presentinvention will no doubt become apparent to a person of ordinary skill inthe art after having read the foregoing description, it is to beunderstood that the particular embodiments shown and described by way ofillustration are in no way intended to be considered limiting. By way ofexample, although described supra in terms of adjunctive ultrasoundscreening, in view of the present disclosure one skilled in the artwould readily be able to apply the thick-slice display apparatus of thepreferred embodiments in the context of computerized tomography (CT)and/or magnetic resonance imaging (MRI) environments. In each case,individual image slices generated from CT scans or MRI scans of thebreast are compounded so as to form thick-slice images of slab-likeportions of the breast along planes parallel to a standardized x-raymammogram view plane, and the thick-slice images are displayed in closeproximity to an x-ray mammogram of the breast in a way that allows themto be manually translated and superimposed thereon by the radiologist.The elevation and/or depth CT or MRI thick-slice images may be adjustedby manual joystick control or other control mechanism.

[0067] By way of further example, while described supra in terms of thesuperposition of only a single thick-slice ultrasound image over anx-ray mammogram (or vice versa), in other preferred embodiments two ormore thick-slice ultrasound images are superimposed with the x-raymammogram. Moreover, the two or more thick-slice images may correspondto non-adjacent portions of the breast volume. In still other preferredembodiments, it has been found that useful observations may be made bysuperimposing two ultrasound thick-slice images taken from the sameregion of the breast at different points in time, e.g., spaced 1 yearapart, to assist in screening for changes in the breast over time. Thetwo superimposed thick-slice images may be superimposed upon an x-raymammogram image, or alternatively can be displayed without the x-raymammogram image. In other preferred embodiments, three or morethick-slice ultrasound images are superimposed corresponding to three ormore different points in time. In still other preferred embodiments, aplurality of x-ray mammogram images taken at different points in timecan be superimposed with a plurality of thick-slice ultrasound imagestaken at different points in time. Methods for implementing systemsaccording to these preferred embodiments would be readily apparent tothose skilled in the art in view of the present disclosure.

[0068] By way of further example, while described supra in terms of thesuperposition of images from two different modalities, the features andadvantages of the preferred embodiments are readily applied to thesuperposition of medical images from three different modalities, e.g.,ultrasound, x-ray mammogram, and MRI. According to a preferredembodiment, for those modalities that yield three-dimensionalinformation, thick-slice images are derived therefrom and used foroverlay purposes. Exemplary combinations may include overlays of: (i)x-ray mammogram, ultrasound, and MRI; (ii) (ii) x-ray mammogram,ultrasound, and CT; (iii) CT, ultrasound, and MRI; (iv) CT, x-raymammogram, and MRI; and others. The features and advantages of thepreferred embodiments are also readily applied to the superposition ofmedical images from four or more different imaging modalities. For suchmulti-modality cases, in order to reduce the amount of clutter and toderive more utility from the overlays, the individual medical images arepreferably enhanced prior to or during overlay so as to display the mostsalient features revealed by its respective imaging modality. By way ofexample, the ultrasound image will be spatially low-pass filtered toconcentrate on larger features, it being understood that very smallstructures such as microcalcifications are not strongly revealed by theultrasound modality. The reduced amount of speckle from the low-passfiltering will reduce the amount of clutter in the multi-modalityoverlay image.

[0069] Moreover, it is to be appreciated that the features andadvantages of the preferred embodiments are applicable to medicalimaging formats not currently contemplated for use in large-scale breastcancer screening programs. For example, phase information fromholographically encoded medical images may be interferometricallycombined to achieve the medical image superpositions, or other types oftime- or space-based modulation methods may be used to encode andsuperimpose the medical images. Therefore, reference to the details ofthe preferred embodiments are not intended to limit their scope, whichis limited only by the scope of the claims set forth below.

What is claimed is:
 1. A method for facilitating the detection ofabnormalities in a breast, comprising: displaying an x-ray mammogramimage of the breast to a user; displaying a thick-slice ultrasound imageof the breast near said x-ray mammogram image, said thick-sliceultrasound image representing sonographic properties of a slab-likevolume within the breast occupying less than the entire breast volume;and overlaying one of said ultrasound image or said x-ray mammogramimage over the other to form a bimodal image, said bimodal imagefacilitating user perception of structures within the breast.
 2. Themethod of claim 1, said x-ray mammogram image corresponding to astandard x-ray mammogram view plane, said slab-like volume beingsubstantially parallel to said standard x-ray mammogram view plane. 3.The method of claim 2, said thick-slice ultrasound image being displayedon an electronic display device, further comprising dynamically varyinga thickness of said slab-like volume responsive to a first user controlinput.
 4. The method of claim 2, further comprising dynamically varyingan elevation of said slab-like volume relative to a reference planeparallel to said standard x-ray mammogram view plane responsive to asecond user control input.
 5. The method of claim 1, said one of saidultrasound image or said x-ray mammogram image being an overlying imageand said other being an underlying image, said overlaying furthercomprising: moving said overlying image onto said underlying image froman initial nearby position such that said overlying and underlyingimages are in at least approximate registration; and performing verniershifts to a position of said overlying image relative to said underlyingimage under manual control of the user, said vernier shifts facilitatinguser perception of structures within the breast.
 6. The method of claim5, one of said overlying or underlying images being displayed on anelectronic display device, wherein said moving said overlying image isexecuted by a processor according to an automated registration method.7. The method of claim 5, wherein said moving said overlying image isexecuted under manual control of the user.
 8. The method of claim 7,said moving said overlying image comprising: identifying at least onenatural watermark within the breast tissue visible on both of saidoverlying and underlying images; and aligning said overlying image oversaid underlying image using said natural watermark.
 9. The method ofclaim 8, said natural watermark comprising a calcification.
 10. Themethod of claim 5, said performing vernier shifts comprising, if saidoverlying and underlying images are already in perfected registration,shifting said overlying image by a small amount such that said imagesare not in perfected registration, and then shifting said overlyingimage back into perfected registration, said shifting facilitating userperception of structures within the breast.
 11. The method of claim 5,said overlying and underlying images both being hardcopy images, theoverlying image being imprinted upon a translucent medium to allow atleast partial visibility of the underlying image, said overlaying beingperformed by direct hand control of the hardcopy images.
 12. The methodof claim 5, said underlying image being displayed on a computer monitor,said overlying image being displayed in hardcopy format on a translucentmedium.
 13. The method of claim 5, said overlying and underlying imagesboth being displayed on a computer monitor, said overlaying comprisingpixelwise mixing of said overlying and underlying images according to apredetermined mixing algorithm.
 14. The method of claim 13, wherein saidmanual control is implemented using a control device selected from thegroup consisting of: joystick, trackball, computer mouse, andtouchscreen.
 15. The method of claim 13, wherein said predeterminedmixing algorithm comprises at least one mixing factor that isdynamically user-adjustable, user adjustment of said mixing factor alsofacilitating user perception of the breast structures.
 16. A method forfacilitating the detection of abnormalities in a breast, comprising:displaying an x-ray mammogram image of the breast to a user; displayingan ultrasound image of the breast near said x-ray mammogram image;overlaying one of said ultrasound image or said x-ray mammogram imageover the other such that said images are in at least approximateregistration; and shifting a position of said overlying image relativeto said underlying image by incremental amounts under manual control ofthe user, said shifting facilitating user perception of structureswithin the breast.
 17. The method of claim 16, said one of saidultrasound image or said x-ray mammogram image being an overlying imageand said other being an underlying image, said overlaying comprisingmoving said overlying image into said approximate registration with saidunderlying image, said shifting by incremental amounts being performedsubsequent to said moving into approximate registration.
 18. The methodof claim 17, wherein said moving into approximate registration isexecuted by a processor according to an automated registration method.19. The method of claim 17, said shifting by incremental amountscomprising, if said overlying and underlying images are in substantiallyperfect registration, perturbing and then restoring said substantiallyperfect registration, said perturbing and restoring facilitating userperception of structures within the breast.
 20. The method of claim 17,wherein said moving into approximate registration is executed undermanual control of the user.
 21. The method of claim 20, said moving intoapproximate registration comprising: identifying at least one naturalwatermark within the breast tissue visible on both of said overlying andunderlying images; and aligning said overlying image over saidunderlying image using said natural watermark.
 22. The method of claim21, said natural watermark comprising a calcification.
 23. The method ofclaim 16, said x-ray mammogram image corresponding to a standard x-raymammogram view plane, said ultrasound image being a thick-slice imagerepresenting sonographic properties of a slab-like volume of the breastsubstantially parallel to said standard x-ray mammogram view plane. 24.The method of claim 23, wherein said slab-like volume occupies less thanan entire volume of the breast.
 25. The method of claim 24, saidthick-slice image being displayed on an electronic display device,further comprising dynamically varying a thickness of said slab-likevolume responsive to a first user control input.
 26. The method of claim24, further comprising dynamically varying an elevation of saidslab-like volume relative to a reference plane parallel to said standardx-ray mammogram view plane responsive to a second user control input.27. The method of claim 17, said overlying and underlying images bothbeing hardcopy images, the overlying image being imprinted upon atranslucent medium to allow at least partial visibility of theunderlying image, said overlaying being performed by direct hand controlof the hardcopy images.
 28. The method of claim 28, said underlyingimage also being imprinted on a translucent medium, said underlying andoverlying images being displayed on a lightbox.
 29. The method of claim17, said underlying image being displayed by backprojection onto alightbox, said overlying image being imprinted upon a translucent mediumand manually placed on said lightbox.
 30. The method of claim 17, saidoverlying and underlying images both being displayed on a computermonitor, said overlaying comprising pixelwise mixing of said overlyingand underlying images according to a predetermined mixing algorithm. 31.The method of claim 17, wherein said manual control is implemented usinga control device selected from the group consisting of: joystick,trackball, computer mouse, and touchscreen.
 31. The method of claim 17,said overlying and underlying images both being displayed on a computermonitor, said overlaying comprising pixelwise mixing of said overlyingand underlying images according to a predetermined mixing algorithm. 32.The method of claim 31, wherein said manual control is implemented usinga control device selected from the group consisting of: joystick,trackball, computer mouse, and touchscreen.
 33. The method of claim 31,wherein said predetermined mixing algorithm comprises at least onemixing factor that is dynamically user-adjustable, user adjustment ofsaid mixing factor also facilitating user perception of the breaststructures.
 34. An apparatus for facilitating analysis of a breast usingan x-ray mammogram image thereof and ultrasound information derived fromultrasonic scans of the breast, comprising: a display device; and aprocessor coupled with said display device and generating for viewingthereon a display output, said display output comprising a superpositionof a thick-slice ultrasound image and the x-ray mammogram image, saidthick-slice ultrasound image representing sonographic properties of aslab-like volume within the breast occupying less than the entire breastvolume.
 35. The apparatus of claim 34, said x-ray mammogram imagecorresponding to a standard x-ray mammogram view plane, said slab-likevolume being substantially parallel to said standard x-ray mammogramview plane.
 36. The apparatus of claim 35, further comprising an inputdevice coupled with said processor for receiving user inputs, saidprocessor dynamically varying a thickness of the slab-like volumeresponsive to a first user input.
 37. The apparatus of claim 36, saidprocessor dynamically varying an elevation of the slab-like volumeresponsive to a second user input.
 38. The apparatus of claim 34,further comprising an input device coupled with said processor forreceiving user inputs, said superposition of the thick-slice ultrasoundimage and the x-ray mammogram image being characterized by an alignmentamount ranging from completely non-overlapping to perfectly registered,said processor executing a coarse alignment procedure to change saidalignment amount from completely non-overlapping to at leastapproximately registered, said processor executing a vernier alignmentprocedure subsequent to said course alignment procedure under directmanual control of the user, user observation of said display outputduring said vernier alignment procedure facilitating user perception ofbreast structures.
 39. The apparatus of claim 38, said input devicecomprising a direct manual control input for receiving said directmanual controls, said direct manual control input being selected fromthe group consisting of: joystick, trackball, computer mouse, andtouchscreen.
 40. The apparatus of claim 38, wherein said processorperforms said coarse alignment procedure according to an automatedregistration method.
 41. The apparatus of claim 38, wherein saidprocessor performs said coarse alignment procedure under direct manualcontrol of the user.
 42. The apparatus of claim 34, further comprisingan input device coupled with said processor for receiving user inputs,said superposition being generated according to a predeterminedpixelwise mixing algorithm including a mixing factor that is dynamicallyuser adjustable according to a third user input, said user adjustment ofsaid mixing factor also facilitating user perception of the breaststructures.
 43. An apparatus for facilitating analysis of a breast usingan x-ray mammogram image thereof and ultrasound information derived fromultrasonic scans of the breast, comprising: a display device viewable bya user; an input device; and a processor coupled with said input deviceand with said display device, said processor generating and providing adisplay output to said display device, said display output comprising asuperposition of the x-ray mammogram image and a two-dimensionalultrasound image derived from the ultrasound information, saidsuperposition being characterized by an alignment amount, said processoradjusting said alignment amount according to direct manual manipulationsof said input device by the user, user observation of said displayoutput during said alignment adjustments facilitating user perception ofbreast structures.
 44. The apparatus of claim 43, said input devicebeing selected from the group consisting of: joystick, trackball,computer mouse, and touchscreen.
 45. The apparatus of claim 43, saidultrasound image being a thick-slice ultrasound image representingsonographic properties of a slab-like region within the breast occupyingless than the entire breast volume.
 46. The apparatus of claim 45, saidx-ray mammogram image corresponding to a standard x-ray mammogram viewplane, said slab-like region being substantially parallel to saidstandard x-ray mammogram view plane.
 47. The apparatus of claim 46, saidprocessor dynamically varying a thickness of the slab-like regionresponsive to a first user input.
 48. The apparatus of claim 46, saidprocessor dynamically varying an elevation of the slab-like volumeresponsive to a second user input.
 49. The apparatus of claim 46, saidsuperposition being generated according to a predetermined pixelwisemixing algorithm.
 50. The apparatus of claim 49, said mixing algorithmincluding a mixing factor that is dynamically user adjustable accordingto a third user input, said user adjustment of said mixing factor alsofacilitating user perception of breast structures.